Low-voltage rivet heater



Dec. '16, 1947. J. B. LOE

LOW VOLTAGE HIVET HEATER Filed March 9, 1945 L/lwfin Bulge! L 06 INVENTOR. 1% ATTORJYEY Patented Dec. 16, 1947 UNITED STATES ATE'NT OFFICE LOVV-VOLTAGE RIVET HEATER Application March 9, 1945,, Serial No. 581,775

This invention relates to an electric heating device for applying intense heat to predetermined positions and more particularly to such a device for firing explosive rivets.

Explosive rivets have assumed an important position in the field of fasteners of adjacent metal sheets and other articles. In 'such fasteners, an explosive charge is introduced into a cavity in the rivet, said charge being adapted on firing to expand or bulge the walls of the rivet outward and thus secure the sheets firmly together;

While the explosive charges in such rivets may be fired by various procedures, one common method consists in applying a heated surface to the head of the rivet, thereby heating the entire rivet by conduction to the explosion temperature of the charge. A number of different types of apparatus have been employed for firing rivet charges but no one of these has been entirely satisfactory, because of cumbersome apparatus, too rapid deterioration in use, slowness of heating, overheating of parts of the apparatus, and the like.

An object of the present invention is a novel and improved apparatus for the application of intense heat to predetermined positions. A further object is a heating device for the firing of explosive rivets characterized by simplicity, compactness and moderate bulk. A still further object is such a device having a durable firing tip,

capable of rapid heating, and so designed as to promote the rapid cooling of the conducting elements adjacent to said tipv without loss of emciency in the use. of the device. Additional ob jects will be disclosed as the invention is described more at length. hereinafter.

I havefound that the foregoing objects are accomplished when I employ an electric heating device comprising a heating element or tip of a material of relatively high resistivity, two metal leads characterized by good conductivity and connected conductibly to said heating element and insulated from one another, and a non-conducting handle attached to the ends of the leads farthest removed from the heating element.

Electrical connections are present so that the passage of electric current through the condoctors and heating element can be controlled and the heating element tip raised to glowing heat. An important feature of the apparatus is the provision of passageways longitudinally through each of the metallic leads and connection of these passageways to a compressed air supply so that air can be forced through these passageways to exert a cooling effect.

. The principles and details of construction and 2 Claims. (Cl. 219-21) operation of the firingdevice according to the invention will be seen more readily by reference to the accompanying drawing. Figure 1 is a side elevation of the device, showing generally its appearance and connection to the source of electric current. Figure 2 is a top View of the device itself.

In Figure 1, I designates a heating element terminating in a tip 2 of reduced dimensions, the heating element being of a material of relatively high resistivity and good heat stability such as a nickel-chromium alloy. This heating element is secured in conductible relationship to tWo alu inurn conductor leads, of which only 5 is seen in this figure. These leads are secured at the end farthest from the heating element to the handle by screws iii. This handle has the open space Is to allow ready gripping of the same and a trigger or push button arrangement l9 extending thereinto which allows the closing of an electric circuit by pressure of the finger on said button. In this circuit 29, the plug 2| may be inserted in a standard outlet. When the circuit is closed at l9, the high voltage alternating current is stepped down at transformer 22, and low voltage, high amperage current flows through cables 23 and 25 to the leads 5 and 5, thence to the tip of the heating element.

Figure 2, a top View of the device, shows more specifically the features of the invention, The heating element I terminates in the tip 2 of reduced cross section, this being of a metal of relatively high resistance as stated previously. The divided heating element is brazed at 3 and 3' to the copper bars 4 and 4', which are secured conducti'bly to the aluminum conducting leads 5 and 5' by the bolts 6 and 6'. The aluminum leads are insulated from one another by the separating mica strip or strips 1. The aluminum lead bars are of rugged construction and of sufficient dimensions to give good conductivity. These bars are characterized by having relatively deep longitudinal grooves or passageways 8 therethrough, five such grooves being shown in the drawing in each lead. These grooves extend to the upper surface of each bar so that these latter substantially comprise thin strips of metal separated by air spaces. At the end of the bars farthest removed from the tip. an open passage or hole 9 passes transversely through the two bars, exiting by separate openings into each of the grooves 8. This hole 9 is connected with air inlet Ill. The grooves in the lead bars are covered at the top by a strip of a rigid, nonconducting material I I, for example of Bakelite, this cover being held firmly in place and in air-tight relationship by screws 12. At the end of the cover strip nearest the heating element, separate small openings [3 lead through the strip into each of the passageways through the bars, Where the transverse passage 9 through said bars connects the two, a nonconducting bushing l4 provides connection and confinement. With the arrangement shown, cooling air may be forced through the leads, entering at l and exiting at the farther end at the openings i3. Desirably the air inlet will be into the bottom of one of the aluminum leads, and I find it desirable to have the holes in this lead from the through hole to the separate passageways smaller in diameter than those in the lead farther removed. In this way a more uniform distribution of the cooling air is assured, The lead bars are fastened to the handle 6 of nonconducting material by screws l6, and also are held firmly in back against the handle. A bolt I! holds the cables '23 and 24 to the bars and 5'. While a cover over the passageways, otherwise open at the top, has been shown in the drawing, this is not essential, as the passages through the metal may be closed by the metal itself at said top, opening only at the far end.

As has been brought out, the heating device of the present invention is intended for use with low voltage, high amperage electric current, with conversion of the electrical energy into high temperature heat at a localized place of application, for example temperatures of around 350 to 550 C. The device has characteristics that give it superiority in performance over other previously described apparatus for the purpose. The ready cooling of the leads during operation makes it possible to reduce the heat flow from tip to cable and transformer, that is, to maintain a lower cable and transformer temperature and to obtain an apparatus more convenient for use and of lighter weight, hence more readily operable.

One of the more important places of application of the apparatus is in the firing of explosive rivets. In such use the heating element tip is brought to the desired elevated temperature and held firmly against the head of the rivet. The temperature of the rivet is thus raised to the firing temperature of the explosive charge, and the rivet is then expanded in the desired manner.

The device may be applied, however, to any other I use where localized application of intense heat is desired.

My improved apparatus has been described fully in the foregoing. It will be understood, however, that many variations in details of design and arrangement may be introduced without departure from the scope of the invention. The electrical circuit shown, for example, has used the switch in the handle of the apparatus for controlling directly the electrical circuit. It may, however, seem desirable to have this switch merely operate a second magnetically-controlled switch or relay. Furthermore, in place of the nickel-chromium alloy tip, other suitable metals may be used, for example Monel metal, stainless steel, Manganin, nickel-chromium-iron alloys, etc.

I intend to be limited only by the following claims.

I claim:

1. An apparatus for the firing of explosive rivets electrically comprising two metallic conductors insulated from one another, a heating element connected conductibly to one end of said conductors, a nonconducting handle attached to the other ends of said conductors, electrical connections whereby the controlled passage of low voltage, high amperage electric current through said conductors brings the heating element to the desired high temperature, a plurality of longitudinal passageways closed at the top through each of said conductors, separate openings into each of said passageways from an air supply line at the end of the conductors nearest the handle, and separate exit openings from each of said passageways at the end toward the heating element, whereby cooling air may be forced through a substantial portion of the length of the conductors and in efiective heat exchange relationship therewith.

2. The apparatus of claim 1, in which the main cooling air supply line goes directly into one of the metallic conductors and to a passageway transversely across both of said conductors at the end nearest the handle, said passageway exiting into each of the longitudinal passageways by a plurality of openings, the exit openings into the longitudinal passageways in the conductor into which the air line first enters being smaller than the exit openings in the second conductor.

JUSTIN BUNYAN LOE.

REFERENCES. CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,491,389 Frykman Apr. 22, 1924 2,080,220 Butter et al May 11, 1937 2,200,322 Arnesen May 14, 1940 2,350,614 Jackson June 6, 1944 

